This invention relates to a simplified single-stage process for the production of polyamines containing primary amino groups by the hydrolysis of compounds containing isocyanate groups (NCO-content 0.5 to 40 wt. %) with water in the presence of a catalyst and a water-soluble solvent. The invention also relates to amines produced by this process.
It is known that aromatic isocyanates can be converted into primary aromatic amines by acid hydrolysis. However, because the amine formed during hydrolysis further reacts with unreacted isocyanate to form the corresponding urea, the yield of primary amine is less than desirable. This further reaction with isocyanate cannot be suppressed even by using excess strong mineral acid. A fairly recent example of such a procedure may be found in Japanese Patent No. 55 007-827.
DE-B No. 1,270,046 describes a process for the production of primary aromatic amines containing polyalkylene glycol ether segments. In this disclosed process, reaction products of aromatic diisocyanates or triisocyanates with polyalkylene glycol ethers and/or polyalkylene glycol thioethers (preferably those having molecular weights of from 400 to 4000) are further reacted with secondary or tertiary carbinols. The products are subsequently subjected to thermal decomposition at elevated temperatures in an inert solvent (optionally in the presence of acid catalysts). In addition to the high decomposition temperature, another disadvantage of this procedure is that inflammable, readily volatile alkenes which are explosive in admixture with air are formed during the thermal decomposition of the urethanes so that safety measures have to be taken.
DE-B No. 1,694,152 describes the production of prepolymers containing at least two terminal amino groups. In the disclosed process, hydrazine is reacted with aminophenyl ethylamine or other diamines and an NCO-prepolymer of a polyether polyol and polyisocyanate (NCO:NH ratio=1:1.5 to 1:5). Unreacted amine must be carefully removed in another step because it catalyzes the reaction with polyisocyanates to a considerable extent, thereby leading to short processing times.
Another possible method for synthesizing polyamines containing urethane groups is described in French Patent No. 1,415,317. NCO-prepolymers containing urethane groups are converted with formic acid into the N-formyl derivatives. These N-formyl derivatives are then hydrolyzed to form terminal aromatic amines. The reaction of NCO-prepolymers with sulfamic acid also leads to compounds containing terminal amino groups (DE-PS No. 1 155 907). Relatively high molecular weight prepolymers containing aliphatic secondary and primary amino groups are obtained according to DE-B No. 1,215,373 by reacting relatively high molecular weight hydroxyl compounds with ammonia under pressure at elevated temperature in the presence of catalysts. U.S. Pat. No. 3,044,989 teaches production of such prepolymers by reacting relatively high molecular weight polyhydroxyl compounds with acrylonitrile, followed by catalytic hydrogenation. Relatively high molecular weight compounds containing terminal amino groups and urethane groups may also be obtained by reacting NCO-prepolymers with enamines, aldimines or ketimines containing hydroxyl groups, followed by hydrolysis (DE-A No. 2,546,536 and U.S. Pat. No. 3,865,791). Another possible approach to synthesizing aromatic polyamines containing urethane and ether groups is opening the ring in the reaction of isatoic acid anhydride and diols. Polyamines of this type are described, for example, in U.S. Pat. No. 4,180,644 and in DE-A Nos. 2,019,432; 2,619,840; 2,648,774 and 2,648,825. The poor reactivity of aromatic ester amines obtained in this way is, however, a disadvantage in numerous applications.
The reaction of nitroaryl isocyanates with polyols, followed by reduction of the nitro groups to aromatic amino groups, is also known (U.S. Pat. No. 2,888,439). The main disadvantage of this process is the high cost of the reduction step.
It is also known that certain heteroaromatic isocyanic acid esters can be converted into heteroaromatic amines by basic hydrolysis. Unfortunately, the hydrolysis conditions described by H. John in J. Prakt. Chemie 130, 314 et seq and 332 et seq (1931) for two specific, heteroaromatic monoisocyanic acid esters are unsuitable for the conversion of poly-NCO-compounds into aliphatic and/or aromatic amines and they are also dangerous.
Two of our own proposals (DE-A Nos. 2,948,419.3 and 3,039,600.0) are directed to multistage processes for the production of polyamines. In our processes, NCO-preadducts are subjected to alkaline hydrolysis with excess base (alkali hydroxides) to form carbamates. These carbamates are then decomposed by acidification with mineral acids or ion exchanger resins in equivalent quantities or in quantities exceeding the quantity of base optionally followed by neutralization of excess quantities of acid with base and subsequent isolation of the polyamines.
These known processes for the production of polyamines are all somewhat complicated. It would therefore be desirable to have a technically simple process for the production of polyamines which is also economically more favorable. To this end, a single-stage process rather than the customary multistage processes would be particularly advantageous. It would also be advantageous to have a process in which virtually no salts are formed and no filtration step is required.
Until now, all attempts to obtain satisfactory yields of polyamines by the direct hydrolysis of polyisocyanates in a single stage have been unsuccessful. Instead of the desired hydrolysis products, the products obtained by known processes are not homogeneous nor are they free flowing and they contain urea groups with very few, if any, amino groups (cf. Comparison Examples). The reason for this may lie in the fact that the isocyanate/amine reaction is considerably faster than the isocyanate/water reaction. Consequently, the hydrolysis reaction catalyzed by alkali hydroxides has generally been carried out at the lowest possible temperatures and the alkali carbamates formed have been subsequently decomposed by heat treatment or by treatment with an acid.